Recent image forming apparatuses are provided with the function of embedding information to a confidential document, which may be used to prevent the confidential document from being copied, for example, as described in the U.S. Pat. Nos. 5,604,596, 5,798,844, 5,486,686, and 5,647,010, the US Patent Application Publication No. 2005/078331 and the Japanese Patent Application Publication No. 2001-086330.
Further, information being embedded into a confidential document may be used to trace the confidential document. In one example, information regarding a user who creates the confidential document may be embedded at the time of generating the confidential document. In another example, the Japanese Patent Application Publication No. H11-355557 discloses a technique that embeds information regarding a user who copies the confidential document at the time of copying the confidential document. Such information may be used to trace the confidential document when the confidential document is leaked to a third person.